Hybridization is not uncommon in this genus. Hybrid plants can be recognized by low fruit set and frequently by their elongated spikelets (it has been hypothesized that the spiklet axis continues to elongate when resources are not devoted to fruit formation). The perianth bristles are usually either retrorsely barbellate (at least near the tip) or highly bent and contorted. These features help to separate the bristles from the filaments, which may be persistent on the fruits. References: Schuyler (1967), Whittemore and Schuyler (2002).

2b.
Leaves 3–12 on each stem; floral scales green-brown or brown to black, elliptic to broad-elliptic; spikelets cylindrical or narrow-ellipsoid to narrow-ovoid or ovoid (rarely broad-ovoid, as sometimes in
S. cyperinus)

8a.
Perianth bristles largely contained within the floral scales, even in fruit, and therefore not obviously visible; achenes 1–1.2 mm long; floral scales with evident green midribs, even at maturity of the fruit

11a.
Involucels and base of involucral bracts very dark brown to black; stems mostly 1–3 mm thick below the inflorescence; leaf blades 2–5 mm wide; floral scales rounded at apex or with a very tiny mucro to 0.05 mm long; achenes maturing late June through early July